| Title | Using computed tomography (CT) to reconstruct depositional processes and products in the subaqueous glacigenic Champlain Sea Basin, Ottawa, Canada |
| |
| Author | Al-Mufti, O N ;
Arnott, R W C; Hinton, M J; Alpay, S; Russell, H A J |
| Source | Geomorphology vol. 403, 108165, 2022 p. 1-17, https://doi.org/10.1016/j.geomorph.2022.108165  Open Access |
| Image |  |
| Year | 2022 |
| Alt Series | Natural Resources Canada, Contribution Series 20210355 |
| Publisher | Elsevier |
| Document | serial |
| Lang. | English |
| Media | paper; digital; on-line |
| File format | pdf |
| Province | Ontario |
| NTS | 31G/11; 31G/12 |
| Area | Ottawa |
| Lat/Long WENS | -76.0000 -75.0000 45.7500 45.5000 |
| Subjects | mathematical and computational geology; hydrogeology; Science and Technology; varves; deglaciation; meltwater channels; groundwater discharge; Champlain Sea; Quaternary |
| Illustrations | location maps; satellite images; distribution diagrams; stratigraphic columns; images; schematic diagrams |
| Program | Groundwater Geoscience Archetypal Aquifers of Canada |
| Program | Public
Safety Geoscience Intraplate Earthquakes |
| Released | 2022 02 18 |
| Abstract | In this study, depositional conditions in the glaciogenic Champlain Sea basin were inferred solely from evidence of computed tomography (CT). CT-scan images and Hounsfield unit (HU) profiles of two
continuous cores in Ottawa, Canada, provided the data to identify five lithologically distinct, mud-dominated stratal units. Distinctively, all strata exhibit a repeating pattern of HU values. The upward increase and then decrease in HU values within
each bed suggests upward increasing and then decreasing silt content, which collectively, is interpreted to reflect the consistent waxing followed by waning flow conditions during a single cycle of glaciogenic meltwater discharge. Mud rhythmites at
the base of the succession (Unit 1) and beds of well-stratified mud at the top (Unit 4a) exhibit well-developed parallel-stratification in the lower part of each bed; they are characterized by a range of ~250-350 HU. This wide range in HU values
reflects the effective partitioning of silt-rich and clay-rich parts in each bed, and therefore bed-surface and near-bed transport processes that sorted sediment mostly by grain size, followed by low-energy sediment fallout. The silt-rich part of
each bed was deposited by glaciogenic meltwater-sourced hyperpycnal flows, which due to the freshwater composition of the basin, or at least in the upper part of the water column, were able to plunge to the basin floor and sort particles along the
bed. In comparison, beds of bioturbated mud (Unit 2), banded mud (Unit 3), and diffusely stratified or structureless mud (Unit 4a) have a narrower range of ~50-120 HU, indicative of poorer particle sorting. These conditions, most clearly illustrated
by the bioturbation, indicate a change to a seawater basin that caused meltwater inflows to instead form buoyant, sediment-laden hypopycnal flows, which aided by clay-silt particle flocculation and/or settling-driven convection, resulted in sediment
deposition directly from suspension. In addition to characteristic sedimentary structures and textures, beds within each unit also exhibit similar thickness, which often doubles or triples in the abrupt transition from one unit to the next. These
changes most probably reflect abrupt and systemic changes in deglacial dynamics and its control on sediment supply that often coincide with equally abrupt changes in salinity in the Champlain Sea basin. |
| Summary | (Plain Language Summary, not published)
Sediments from two continuous drill cores in Ottawa, Canada were studied using computed tomography (CT) to reconstruct sediment deposition in the glacial
Champlain Sea basin. Five distinct, mud-dominated units are described. Distinctively, all strata exhibit a repeating pattern that is interpreted to reflect the annual cycle of glacial discharge. Mud rhythmites at the base of the succession (Unit 1)
and beds of well-stratified mud at the top (Unit 4a) are characterized by silt-rich and clay-rich parts in each bed that indicate transport processes that effectively sorted sediment mostly by grain size. These processes reflect the freshwater
composition of the basin, or at least in the upper part of the water column. In comparison, beds of bioturbated mud (Unit 2), banded mud (Unit 3), and diffusely stratified or structureless mud (Unit 4b) indicate poorer particle sorting. These
conditions, most clearly illustrated by the bioturbation, indicate a change to a seawater basin. |
| GEOSCAN ID | 329039 |
|
|